Laminated packaging material for paper container

ABSTRACT

A paper packaging container is formed from the packaging material comprising constitution layers of at least an outside thermoplastic material layer, a paper substrate layer, and an inside thermoplastic material layer, wherein the inside thermoplastic material layer contains at least a linear low density polyethylene, and has properties parameters of an average density of 0.900–0.930, a predetermined peak melting point, a melt flow index of 5–15, and a swelling ratio of 1.3–1.8. The use of the packaging material allows easy filling and packaging to the packaging container and quick heat sealing, and results in more toughly and strongly sealed container, and the material can be used for achieved good sealing independently of the temperature of food contents and thus maintaining the non-scalping and quality preservability of the content product.

TECHNICAL FIELD

This invention relates to a packaging material for paper containerssuitable for filling packaging of liquid foods.

In detail, this invention relates to the packaging material for thepaper packaging container of brick shape and the paper packagingcontainer of a gable top shape suitable for filling packaging of liquidfoods. About the paper packaging container of brick shape, thecontinuous packaging material is longitudinal-sealed in the longitudinaldirection of the packaging material, and the paper packaging material isformed to a tube shape. Products, such as fruit juice, tea, and liquiddairy products, are packed in tube-like packaging material. Atransversal seal is formed in the transversal direction of tube-likepackaging material for every predetermined interval, and the packagingmaterial is cut along the transversal-seal zone. About the paperpackaging container of a gable top shape, paper packaging material iscut in the predetermined shape, and the blanks sealed to containerlengthwise is obtained, and after sealing the bottom of the blank, aliquid food product is packed from the top opening, and the upper partis sealed and the packaging container is obtained.

BACKGROUND ART

The packaging container for milk, juice, or other drinks is obtained asfollows: For example, paper/plastics laminated packaging material withcrease lines are formed to a tube shape by the longitudinal seal of alongitudinal direction. The product is packed in the packaging materialformed by the tube shape, the tube-like packaging material istransversally sealed in the transversal direction of the packagingmaterial, and packaging material is formed in the primary shape of acushion form, or pillow shape, and the packaging material is separatelycut at fixed spacing (when packaging material is a web shape), and thepackaging material is formed to the final shape by folding of a creaseline. The final shape includes a brick shape, a multiple column, ahexagon-head column, tetrahedron shape with four triangular faces, etc.

Furthermore, with the paper packaging container of a gable top shape, apaper packaging material is cut in the predetermined shape, and theblank sealed to container lengthwise is obtained, and after sealing thebottom of a blanks within a filling machine, the product of cow's milk,juice, or other drinks is packed from the top opening, and the upperpart is sealed and the container is obtained. The innermost layer of thepackaging material corresponding to a transversal-seal portion or/, anda longitudinal-seal portion in the paper containers is heat sealed withthe innermost layer of another side, or the outermost layer.

The low density polyethylene (LDPE) by the high-pressure method/printingink layer/paper (fibrous) substrate layer/LDPE/aluminum foil(Al)/LDPE/LDPE, LDPE/printing ink layer/paper substrate layer/LDPE/LDPE,a printing ink layer/LDPE/paper substrate layer/LDPE/LDPE andLDPE/printing ink layer/paper substrate layer/LDPE/aluminum/polyester(PET) is known about the packaging laminate used for the conventionalpaper packaging container product. They are also actually used widelycurrently.

However, LDPE used above is high-pressure method low densitypolyethylene, the low molecule component contained in the high-pressuremethod low density polyethylene of an innermost layer bleeds to the foodcontent in the paper container, and if it preserves at a long period oftime, it has a risk that the taste of a content may change. Moreover, inthe ethylene alpha olefin copolymer obtained using a Ziegler catalyst,the seal temperature is high and the processability is poor. When alubricant is added in order to improve them, the lubricant will bleedinto the food content and will reduce the taste.

The paper container with which linear low density polyethylene (LLDPE)is used for the innermost layer is proposed (JP 62-78059A, JP 60-99647A,etc.). LLDPE is very excellent in a shock intensity, a tear strength, acold brittleness ability, a heat-sealing intensity, a hot tuckperformance, etc. However, since heat-sealing start temperature issomewhat high as compared with LDPE, EVA, or an ionomer, LLDPE may beinferior in the converting properties.

On the other hand, the paper containers which has the innermost layer ofthe ethylene alpha olefin copolymer (the so-called metallocene PE,mLLDPE) polymerized by the metallocene catalyst are proposed (JP7-148895A, JP 8-337237A, JP 9-29868A, JP 9-52299A, JP 9-76435A, JP9-142455A, JP 9-86537A, JP 9-76375A, etc.). It is known that metallocenePE is good for a health performance and can be applied to a containersince the metallocene PE has a low-temperature sealability, the filmprocessability, and a narrow molecular weight distribution (WO 93/No.08221, 44 magazine “plastic” No. 1 60 pages, 39 magazine “chemistryeconomy” No. 9 48 pages, 44 magazine “plastic” No. 10 83 pages).However, even though Metallocene PE has the low-temperature sealability,no metallocene PE can not necessarily make less bleeding out to thecontent in the paper container obtained by heat sealing. Moreover, thegood performance is not shown in an extrusion laminated propertiesrequired for packaging material manufacture, and its convertingproperties.

If liquid food is fruit juice of citrus fruits etc., non-scalping suchas a flavor and tasty, and an oxygen barrier are needed. In the liquidfood, oxygen penetrates through the wall of the carton and, for thereason, those nutritional value is lost. In order to reduce permeationof the oxygen to carton and to make degradation of a nutrient likevitamin C into the minimum, usually an aluminum foil layer is added tolaminated material.

In addition to above-mentioned packaging material, the strip tapecovering the discontinuous section of the innermost layer between twoedges of the packaging material in liquid tight can be provided in thepaper packaging container formed from above-mentioned packagingmaterial. For example, when forming web-like packaging material to atube shape by the longitudinal seal of a longitudinal direction, packingthe filled product in the packaging material, carrying out thetransversal seal of the packaging material in the transversal directionand forming to a brick shape etc. finally, in order to protect thepackaging material edge in a longitudinal-seal portion, the leveldifference section of an innermost layer is covered on a strip tape inliquid tight. Moreover, the hole usually punched at the container wallon top is formed in pouring opening of a packaging container, a spout,and pull tabs. The strip tape (a strip tape patch is included) isattached so that the punched hole may be covered.

As such a strip tape, conventionally, the strip tape of the single layercomposition of the low density polyethylene (LDPE) by the high-pressuremethod, the strip tape which laminated LDPE to both sides on both sidesof an intermediate layer's high-density polyethylene (HDPE), the striptape which laminated LDPE to both sides on both sides of an intermediatelayer's polyester (amorphous PET and PET are included), the strip tapewith the LDPE laminated on both sides of an intermediate layer'spolyethylene vinyl alcohol (EVOH) are used, or are proposed.

Moreover, the various trials in which the practical substitute whichchanges to aluminum foil is developed have been made. Moreover, it canbe scrapped after use, it being provided with the outstanding oxygen gasbarrier, and perfume barrier properties. Using the vapor deposited layerof an inorganic oxide for the packaging material for paper containerswas proposed (JP,5-28190,Y, JP,8-500068,A, JP,6-93120,A). By thepackaging material which has such a gas (oxygen) barrier, the papercontainer which has a non-scalping or quality keeping ability can beoffered. In filling/packing process of liquid food, the surface portionto be sealed is polluted with an oxide by the temperature of the fusedextrusion heat in the extrusion lamination step. Moreover, the surfaceis polluted with remains liquid food. It becomes important in an actualmanufacturing process to optimally seal the packaging material to whichsuch a contaminant and an impurity exist in the surface. In theabove-mentioned conventional liquid food paper container packagingmaterial, it is difficult to obtain the optimal seal.

In the filling packaging method of a brick shape packaging container,the innermost layer of one edge of packaging material and the outermostlayer of the edge of another side are longitudinally sealed for thepackaging material of a continuation paper substrate layer with a creaseline. The packaging material is formed in the longitudinal direction ata tube shape, and filled liquid food is packed in tube-like packagingmaterial. The innermost layer of tube-like packaging material is sealedwith each other under the surface of this liquid food, and thetransversal seal of the packaging material is carried out in thetransversal direction for every predetermined spacing. The packagingmaterial is cut along with a transversal-seal portion, it forms inprimary shape, the packaging material is formed by folding in alignmentwith the crease line in the final shape of a brick shape, and apackaging container is obtained. It is difficult to obtain a good sealby the filling packaging method, since the packaging material is sealedunder the surface of liquid food, liquid food surely remains and thesurface is polluted.

Furthermore, since filling liquid food has various quality andproperties about temperature, the temperature conditions when fillingwith and packaging the food are changed broadly, therefore thetemperature of the filling step is influenced and is changed in therange also with the large seal temperature in the process of filling andpackaging. However, since the heat adhesive resin in the conventionalpackaging material does not necessarily have the seal properties of alarge temperature range, the temperature of a filling content influencesand a good seal is not obtained.

Moreover, in the multi-purpose conventional thermoplastic polymer forseals mentioned above, there is a risk that this thermoplastic materiallayer may melt, a pinhole, foaming, a blister, etc. may happen in somelayers, and seal strength may decrease remarkably, and a liquid contentmay leak from the poor portion, by for example, the elevated-temperatureair under the sealing step. If the layer of a thermoplastic material isthickened in order to prevent them, the container cost risesinconveniently.

DISCLOSURE OF THE INVENTION

This invention was made based on an above-mentioned background. Thepurpose of this invention is offering the packaging material for papercontainers for filling packaging of the liquid food in which thepackaging material has good performance in the extrusion-laminatingproperties and the converting properties required in the case of thepackaging material manufacture, and the packaging material can be easilymanufactured, the packaging material can be quickly heat sealed, theseal is made tougher, the good seal is obtained without the influencefrom the temperature of a filling content, and the packaging materialhas a non-scalping or a quality preservability.

Moreover, the purpose of this invention is offering the packagingmaterial for paper containers by which a pinhole, foaming, a blister,etc. do not happen in some thermoplastic material layer under thesealing step, but seal strength's can be maintained, there is no leakageof a liquid content, and the paper container of low cost ismanufactured.

The above-mentioned subject is solved by the packaging material forpaper containers by this invention. That is, the packaging material forpaper containers by this invention relates to a packaging material forpaper containers including constitution layers of at least an outermostthermoplastic material layer, a paper substrate layer, a barrier layer,and a thermoplastic material innermost layer, in which each constitutionlayer is laminated in the above order. The thermoplastic materialinnermost layer contains at least the linear low density polyethylenewhich has a narrow molecular weight distribution, and is characterizedby having the properties parameter of an average density of 0.900–0.915(preferably 0.905–0.910), 88–103 degrees C. (preferably 93–103 degreesC.) of a peak melting point, a melt flow index of 5–20, a swelling ratio(SR) of 1.4–1.6, and a 20–50 micrometers (preferably 20–30 micrometers)of a layer thickness.

In the desirable embodiment of this invention, the thermoplasticmaterial outermost layer contains at least the linear low densitypolyethylene having a narrow molecular weight distribution, and has theproperties parameter of the average density of 0.900–0.925, 88 –103degrees C. (preferably 93–103 degrees C.) of the peak melting point, themelt flow index of 5–20, the swelling ratio (SR) of 1.4–1.6, and 10–25micrometers (preferably 10–20 micrometers) of the layer thickness.

In another desirable embodiment of this invention, an adhesives layerbetween the barrier layer and the thermoplastic material innermost layercontains at least the linear low density polyethylene having a narrowmolecular weight distribution, and the adhesives layer has theproperties parameter of the average density of 0.900–0.915 (preferably0.905–0.910), 88–103 degrees C. [preferably 93–103 degrees C] of thepeak melting point, the melt flow index of 5–20, the swelling ratio (SR)of 1.4–1.6, and 2–15-micrometer of the layer thickness.

In still more nearly another desirable embodiment of this invention, anadhesive thermoplastic material layer between the paper substrate layerand the barrier layer contains at least the linear low densitypolyethylene which has a narrow molecular weight distribution. Theadhesive thermoplastic material layer has the properties parameter ofthe average density of 0.890–0.925, 88–103 degrees C. (preferably 93–103degrees C.) of the peak melting point, the melt flow index of 10–20, theswelling ratio (SR) of 1.4–1.6, and 10–25 micrometers (typically 10–20micrometers) of a layer thickness.

The paper packaging container of one embodiment by this invention is apaper packaging container formed from the packaging material whichincludes at least constitution layers of a thermoplastic materialoutermost layer, a paper substrate layer, a barrier layer, and athermoplastic material innermost layer, and laminates each of theconstitution layers in above order. The thermoplastic material innermostlayer contains at least the linear low density polyethylene which has anarrow molecular weight distribution, and has the properties parameterof an average density of 0.900–0.915 (preferably 0.905–0.910), 88–103degrees C. (preferably 93–103 degrees C.) of peak melting point, meltflow index of 5–20, swelling ratio (SR) of 1.4–1.6, and 20–50micrometers (preferably 20–30 micrometers) of layer thickness.

At least, a sealing-surface layer of a strip tape which covers thediscontinuous section of the thermoplastic material innermost layerbetween two edges of the packaging material in liquid tight contains atleast the linear low density polyethylene which has a narrow molecularweight distribution. Furthermore, a sealing-surface layer has theproperties parameter of average density of 0.900–0.915, 88–103-degree C.of peak melting point, melt flow index of 5–20, swelling ratio (SR) of1.4–1.6 (preferably 1.45–1.55), and 20–100-micrometer of layerthickness.

Furthermore, another paper packaging container by this invention is apaper packaging container formed from the packaging material whichcontains constitution layers of at least an outside thermoplasticmaterial layer, a paper substrate layer, and an inside thermoplasticmaterial layer. The inside thermoplastic material layer contains atleast a linear low density polyethylene, preferably a linear low densitypolyethylene which has a narrow molecular weight distributionpreferably, and has the properties parameter of average density of0.910–0.930 (preferably 0.922–0.927), peak melting point 115 degrees C.or more by the differential scanning calorimetry, melt flow index of5–15 (preferably 9–11), and swelling ratio of 1.3–1.8 (preferably1.45–1.55).

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an outline sectional drawing showing the lamination of oneexample of the packaging material for paper containers of thisinvention.

FIG. 2 is a skeleton drawing of the filling machine which uses thepackaging material for paper containers of this invention.

FIG. 3 is an outline sectional drawing showing the lamination of oneexample of the longitudinal-seal portion of the paper packagingcontainer of this invention.

FIG. 4 is an outline sectional drawing showing the lamination of oneexample of the portion which forms a pull tab in the paper packagingcontainer of this invention.

FIG. 5 is an outline sectional drawing showing the lamination of oneexample of the portion which forms a spout in the paper packagingcontainer of this invention.

FIG. 6 is an outline sectional drawing showing the lamination of theexample of the strip tape used for the paper packaging container of thisinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiment of this invention is shown below. The desirable packagingmaterial for paper containers of an embodiment by this invention is thelaminate which laminated each constitution layer in following order,including at least the constitution layers of the thermoplastic materialoutermost layer, the paper substrate layer, the adhesive thermoplasticmaterial layer, the barrier layer (for example, aluminum), and thethermoplastic material innermost layer.

The paper substrate, which can be used in this invention, is a substratethat it is made from kraft pulp and usually has the outstanding strengthand low absorptivity. As the kind, there are the bleached paper (FBL),the paper which is not bleached (UBL), the duplex paper (DUPLEX) of FBLand UBL, clay coating paper, multi-layer duplex-paper (MB), etc., andany may be used in this invention.

The paper packaging container of one embodiment by this inventioncontains the strip tape which covers the discontinuous section of theinnermost layer between two edges of packaging material in liquid tight.The packaging material is formed by the longitudinal seal in thelongitudinal direction at a tube shape, and a filled product is filledin the packaging material, the packaging material is transversal sealedin the transversal direction, and, finally the packaging material isformed into the shape of a multiple column in the shape of ahexagon-head column etc. to a brick shape. As shown in a FIG. 3, inorder to specifically protect packaging material edge 20 a in thelongitudinal-seal portion of the packaging material 20 and 20 in theabove-mentioned case, the level difference section of an innermost layer26 is covered on the strip tape 27 in liquid tight.

Moreover, as shown in a FIG. 4, in order to form the two-layer pull tabs29 a and 29 b in a packaging container, punched holes 20 b and 20 b areformed in a container wall (usually upper surface). So as that thepunched holes 20 b and 20 b may be covered, the strip tape patch 28seals with an innermost layer 26. Furthermore, as shown in a FIG. 5, inorder to form a spout 30 in a packaging container, punched holes 20 band 20 b are formed in a container wall (usually upper surface). So asthat the punched holes 20 b and 20 b may be covered, the strip tapepatch 28 seals with an innermost layer 26.

The adhesive resin layer used in order to laminate the laminatedpackaging material of this invention contains at least the linear lowdensity polyethylene which has a narrow molecular weight distribution,and is chosen from LLDPE which has a specific properties parameter, anethylene vinyl acetate copolymer (EVA), and an ionomer. In thepreferable embodiment of this invention, the LLDPE as an adhesives layerbetween the barrier layer and the thermoplastic material innermost layercontains at least the linear low density polyethylene having a narrowmolecular weight distribution, and the LLDPE has the propertiesparameter of average density of 0.900–0.915, 88–103-degree C. of peakmelting point, melt flow index of 5–20, and swelling ratio (SR) of1.4–1.6, and 2–15-micrometer of layer thickness. By use of the LLDPE,even if it is extruded at an elevated temperature, the thermoplasticmaterial innermost layer can be well-sealed with various barrier layers.By the LLDPE, an extrusion-laminating properties required in the case ofpackaging material manufacture is improved, good performance is shown inthe converting properties by it, and manufacture of packaging materialbecomes easy.

Moreover, in still more nearly another preferable embodiment, LLDPE asan adhesive thermoplastic material layer between the paper substratelayer and the barrier layer contains at least the linear low densitypolyethylene which has a narrow molecular weight distribution, and hasthe properties parameter of average density of 0.890–0.925,88–103-degree C. of peak melting point, the melt flow index of 10–20,the swelling ratio (SR) of 1.4–1.6, and a 10–25-micrometer of layerthickness. By use of the LLDPE, since the extrusion-laminatingproperties and converting properties in the case of packaging materialmanufacture are excellent, manufacture of packaging material laminatingcan carry out very good.

Furthermore, the coat layer using the synthetic resin of ethylene vinylacetate the copolymer (EVA) which has a metal and an adhesive propertyby the extruding lamination method, or the ionomer (IO) which crosslinked the bridge by the metal ion in between the molecules of anethylene vinyl-methacrylate copolymer can also be laminated as theadhesive layer. About 10–50 micro is suitable for the thickness of theadhesives layer. Preferably, the adhesives layer is EVA or IO of 10micro–18 micro of layer thickness.

The packaging material for paper containers by this invention cancontain at least the printing ink layer provided in the outside surfaceof the semi material which does not laminate the resin outermost layeryet, or the ink layer formed in the outside surface of a sealableoutside resin layer. The ink has the water or oily ink for flexographicprintings, the oily ink for gravure, hardenable ink for offset printing,etc. In the embodiment of the preferable packaging material for papercontainers of this invention, the ink layer contains common components(for example, imine compounds etc.) in part with the component containedin the anchor agent layer in contact with the ink layer.

In the packaging material for paper containers of this invention, thethermoplastic material layer which the packaging material outsidesurface laminated is included. The material layer comprises ofpolyolefin resin, such as polyethylene, polypropylene, and ethylenecopolymer, and has a coextrusion film containing the linear low densitypolyethylene (LLDPE) excellent in the resistance (oil resistance, acidresistance, infiltration resistance, etc.) for a content, the mediumdensity polyethylene, and polyethylene as well as low densitypolyethylene (LDPE).

In the preferable embodiment of this invention, the thermoplasticmaterial outermost layer contains at least the linear low densitypolyethylene which has a narrow molecular weight distribution, and ithas the properties parameter of average density of 0.900–0.925, 88–103degrees C. (preferably 93–103 degrees C.) of peak melting point, meltflow index of 5–20, swelling ratio (SR) of 1.4–1.6, and a 10–25micrometers (preferably 10–20 micrometers) of layer thickness. In casethe innermost layer of one edge of the web-like packaging material whichcontains a paper substrate layer with crease lines, and the outermostlayer of the edge of another side are sealed longitudinally in layersand the material is formed in the longitudinal direction at a tubeshape, by using this material, an innermost layer and the outermostlayer can be quickly heat sealed by the broader-based temperature range,and tougher seal strength is made possible.

In the embodiment of the packaging material for paper containers of thisinvention, it has a barrier layer in the inside laminate of theabove-mentioned packaging material. A barrier layer comprises of atleast one chosen from aluminum foil, a metal/inorganic oxide thin film,the ethylene vinyl alcohol copolymer layer (EVOH layer), the nylonlayer, the polyvinylidence chloride film, and the polyvinylidencechloride coat film. As for the vapor deposited film of the inorganicoxide of the barrier layer, the thin film layer (100–5000 Å in thickness(preferably 200–1000 Å)) of inorganic oxides, such as the silicon oxide,a tin oxide, zinc oxide, an indium oxide, a titanium oxide, and aluminumoxide, is formed in the surface of a thermoplastic resin film with athickness [, such as a polyolefin, nylon, polyester, and polyvinylalcohol] of about 10–30 micro of vacuum deposition, sputtering, thechemical vacuum deposition, the plasma-chemistry vapor deposit (PCVD),etc.

The usual aluminum metal can be used as aluminum which constitutes thealuminum foil of a barrier layer, or the thin film layer of aluminum. Inthis embodiment, there is the method of forming the vapor deposited filmby vacuum deposition methods, such as the ion beam method and anelectron beam method, the sputtering method, etc. as a method of formingthe thin film layer of aluminum.

In order to obtain sufficient shading performance, usually, thethickness of the thin film layer of the above-mentioned aluminum ispreferably 10 nm–200 nm, and is more preferably 20–150 nm in thisinvention.

In the above, all light transmissions fall as the thickness of the thinfilm layer of aluminum becomes thick. If the shading performance of theprinting layer is not taken into consideration, the thickness of thethin film layer of aluminum is set to approximately 80 nm and all lighttransmissions will become 0%.

In this invention, the thickness of the thin film layer of aluminum isadjusted according to necessary physical properties etc., correspondingto the existence of a final packaging form and a printing layer, and itslocation.

Reading the barrier layer which can be used in this invention, the filmof the resin may contain barrier resin layers, such as EVOH andpolyvinyl alcohol, and the resin film which has the vapor deposited filmof an inorganic oxide, or the vapor deposited film of aluminum. Theresin film includes the film of polyester resins, such as apolyethylene-terephthalate film and a polybutylene-terephthalate film,polyamide-resin films, such as nylon6 films, 66 nylon films, 610 nylonfilms, 612 nylon films, 11 nylon films, 12 nylon films, and a polyamidefilm by the condensation of a meta-xylene diamine, a polycarbonate resinfilm, polyolefin resin films, such as polyethylene and polypropylene, apoly vinyl alcoholic resin film, and ethylene-vinyl acetate copolymerfilm, a polyvinyl chloride resin film, polyvinylidence chloride resinfilm, polystyrene resin film, poly (meta) acrylate resin film, polyacrylic nitrile resin film, polyacetal resin film, fluororesin film, andother resin films.

In this invention, a silicon oxide (SiOx), aluminum oxide, an indiumoxide, tin oxide, a zirconium oxide, etc. can be used as an inorganicoxide which constitutes the thin film layer of an inorganic oxide, forexample. Furthermore, in this invention, an inorganic oxide may be themixture of silicon monoxide and silicon dioxide, or a mixture of siliconoxide and aluminum oxide.

In this invention, the methods of forming the thin film layer ofinorganic oxide are the methods of forming the vapor deposited film byvacuum deposition methods, such as the ion beam method and an electronbeam method, the sputtering method, the plasma-chemistry vacuumdeposition (the PCVD method), etc. In the above, in order to obtainsufficient barrier performance, usually, the thickness of the thin filmlayer of an inorganic oxide is 10 nm–200 nm, and is preferably 20–150 nmin this invention. When the thickness of the thin film layer of aninorganic oxide exceeds 150 nm, especially 200 nm, there are risks ofdecline of the barrier the performance by the crack and bend of the thinfilm layer of an inorganic oxide, and also there are troubles ofexpensive material cost.

Preferably, the barrier layer mentioned above is a 5–15-micrometer thinlayer, and has the oxygen permeability of under 5 cc/m² 24 hr atm (23degree-C. 85% RH).

In this invention, the thermoplastic material innermost layer containsat least the linear low density polyethylene which has a narrowmolecular weight distribution, and has the properties parameter ofaverage density of 0.905–0.910 (preferably 0.900–0.915), 88–103 degreesC., peak melting point (preferably 93–103 degrees C.), melt flow indexof 5–20, swelling ratio (SR) of 1.4–1.6, and 20–50 micrometers(preferably 20–30 micrometers) of layer thickness.

In the preferable embodiment of this invention, the linearlow-density-polyethylene content polymer of a sealable innermost layerhas swelling ratio (SR) of 1.4–1.6. The above-mentioned parameter isdescribbed more concretely. The “swelling and swell” indicate thephenomenon in which a cross-sectional area increases immediately afterextrudes comes out of a die orifice, and the volume of the wholeextrudes increases. The swelling ratio in this invention indicates thetransversal dimension of the extrudes out of the die measured on thesame conditions as the measurement conditions in the JIS test method formelt-flow-rate (MFR) measurement (namely, expansion coefficient of adiameter).

In another embodiment of this invention, an inside thermoplasticmaterial layer contains at least linear low-density-polyethylene,preferably the linear low density polyethylene having a narrow molecularweight distribution. Furthermore, the inside thermoplastic materiallayer has the properties parameter of average density of 0.910–0.930(preferably 0.922–0.927), the peak melting point of 115 degrees C. ormore by the differential scanning calorimetry, the melt flow index of5–15 (preferably 9–11), and swelling ratio of 1.3–1.8 (preferably1.45–1.55, more preferably about 1.5). Regarding the peak melting pointby the differential scanning calorimetry, in case of one peak, exceeding115 degree C. of the peak melting point and 0.920 or more of averagedensity are required, and if it is two or more peaks, 0.915 or more ofaverage density and exceeds 115 degrees C. of peak melting points forone of those peaks are required.

The thermoplastic material innermost layer contains the blend polymerswhich contain at least the linear low density polyethylene (mLLDPE)which has the narrow molecular weight distribution, which is polymerizedusing the metallocene catalyst. About the mLLDPE, the ethylenealpha-olefin copolymer which comprises to polymerize using the so-calledmetallocene catalyst can be used. To the conventional catalyst with theuneven active site of the conventional catalyst being called multi-sitecatalyst, since the active site is uniform, the metallocene catalyst isalso called single site catalyst.

Specifically, the resin of mLLDPE contains the ethylene alpha-olefincopolymer which is polymerized using metallocene catalysts, such as atrade name “AFFINITY” by the trade name “EXACT” by the trade name“KERNEL” by Mitsubishi Chemical, Inc., the trade name “EVOLUE” by MitsuiPetrochemical Industries, Ltd., the U.S., and the Exxon chemicalcompany, the U.S., and the Dow Chemical Co., and a trade name “ENGAGE.”

In this invention, as long as the above-mentioned properties parameteris shown, resins other than the mLLDPE resin can be used. Moreover, whenit is difficult to obtain the above-mentioned properties parameter bymLLDPE sole, other polymer components can be blended.

The above-mentioned other polymer is thermoplastic resins, such aspolyolefin resin, such as polyethylene, polypropylene, and an ethylenecopolymer, and a polyester resin. They are the low density polyethylene(LDPE) used conventionally, a linear low density polyethylene (LLDPE)excellent in the resistance (oil resistance, acid resistance,infiltration resistance, etc.) over a content, a medium densitypolyethylene, the coextrusion resin containing polyethylene, etc.

The density of the low-density polyethylene blended above is 0.91–0.93g/cm³. The molecular weight is 1×10² to 1×10⁸, and the melt flow rate(MFR) is 0.1–20 g/10 min. In addition, an additive-free material is usedfundamentally. However, according to applications, various additives,such as an antioxidant, a ultraviolet absorber, an antistatic agent,lubricant, an anti blocking agent, a flameproofing agent, inorganic andan organic filler, a coating material, and a pigment, may be addedsuitably.

The metallocene catalyst of mLLDPE is characterized by a polymerizationactive site being single (single site). The ethylene alpha-olefincopolymer which is polymerized using the catalyst has the outstandingproperties which is not acquired in the ethylene alpha olefin copolymerobtained using the multi-site catalyst of the conventional Zieglercatalyst.

As a typical thing of a single site catalyst, there are a metallocenecatalyst and the so-called Kaminsky catalyst. The metallocene catalystis a catalyst which comprises of a metallocene transition-metal compoundand an organoaluminium compound. As a metallocene transition-metalcompound, although a zirconium compound, a titanium compound, a silicacompound, etc. are mentioned, this invention is not limited to them.Moreover, although, as for an organoaluminium compound, an alkylaluminum and linear/cyclo-alminoxane are mentioned, this invention isnot limited to them. Although the polymerization method has asolution-polymerization method, a vapor-phase-polymerization method, aslurry polymerization method, etc., this invention is not limited tothese.

As for the alpha olefin of the comonomer in copolymerization withethylene, butene-1, hexene-1,4-methyl pentene 1, and an octene 1 arementioned. The alpha olefins may be used sole and may be used as themixture.

The preferable mixing ratio of ethylene and alpha olefin is 1–20 wt. %.Desirably, the density of the polymerized ethylene alpha olefincopolymer is 0.900–0.915 g/cm³, and is preferably 0.905–0.910 g/cm³. Itis because the roll separation performance in the time of film formingand the slipping performance of film become bad if smaller than 0.900g/cm³. Moreover, it is because the plasticity and low-temperaturesealability of film are inferior and seal performance falls by thedensity higher than 0.915 g/cm³. The molecular weight is 1×10³ to 1×10⁶,and melt flow rate (MFR) is 3.0–30 g/10 min (preferably 10–20 g/10 min).The peak melting point is 88–103 degrees C. (preferably 93–103 degreesC.).

In addition, various kinds of antioxidants, a ultraviolet absorber, anantistatic agent, lubricant, an anti blocking agent, a flameproofingagent, inorganic and an inorganic filler, a dye, a pigment, etc. may besuitably added by ethylene alpha-olefin copolymer. The low densitypolyethylene is obtained using the conventional multi-site catalystwhich is a Ziegler catalyst, and is not limited to especially the kindor the polymerized method of a catalyst in this invention.

The packaging material for paper containers of the preferable embodimentof this invention contains at least the linear low density polyethylenewhich has a molecular weight distribution with a narrow innermost layerand, has the properties parameter of average density of 0.900–0.915(preferably 0.905–0.910), 88–103 degrees C. (preferably 93–103 degreesC.) of peak melting point, melt flow index of 5–20, swelling ratio (SR)of 1.4–1.6, and a 20–50 micrometers (preferably 20–30 micrometers) oflayer thickness.

As mentioned above, there is an ethylene alpha-olefin copolymer which ispolymerized using a metallocene catalyst as the thermoplastic materialinnermost layer. The mixture which contains, in this invention, theethylene alpha-olefin copolymer which is polymerized using themetallocene catalyst, and the low density polyethylene which ispolymerized using the multi-site catalyst, in a preferable embodiment,can be used. Any layers other than the innermost layer of a papercontainer are not limited.

The blending ratio of components required in order that the ethylenealpha olefin copolymer polymerized and obtained with the metallocenecatalyst may maintain seal performance, such as salability, and shockresistance is 50 wt. % or more (preferably 55–75 wt. %, more preferably55–65 wt. %). Seal performance or shock resistance good at less than 50wt. % are not obtained, and workability and laminated performancedecline at 65 wt. %.

A blending ratio required to heighten fused tension, such as the filmmoldability of the low density polyethylene from multi-site catalyticpolymerization, is 50 or less wt. % (preferably 45–25 wt. %, morepreferably 45–35 wt. %).

If the above-mentioned range is exceeded, since good seal performanceand good shock resistance will not be obtained, it is not desirable.

Optional methods can be used for the methods of adjusting theabove-mentioned resin, for example, they include the method of kneadingby the biaxial kneading extruder, the roll mill, the Banbury mixer,etc., after blending each component and mixing by the blender, themixer, etc., the dry-blend method in which mixed with pellets.

In the preferable embodiment, it is characterized by including ethylenealpha-olefin copolymer from metallocene catalytic polymerization, andthe low density polyethylene from multi-site catalytic polymerization.The ethylene-alpha olefin copolymer which is polymerized with themetallocene catalyst shows a characteristic narrow molecular weightdistribution (Mw/Mn<=3), i.e., a narrow composition distribution, and isuniform polymer in molecular structure. About the physical properties,the characteristic which is excellent in a tensile strength, an impactstrength-proof, a tear strength, and a low-temperature sealability iskept, and a molecular tangle becomes large with the properties of thehigh fused tension which is one of the characteristics of the lowdensity polyethylene from multi-site catalytic polymerization.Therefore, film moldability and an impurity sealability can be improved.

Moreover, since extrusion film-forming performance is good,concentration of additives, such as lubricant, is made low. By the lowconcentration, the paper container which has the reduction of hindranceagainst the seal performance, maximization of the characteristic of sealperformance, reduction of influence to the taste of the content food bythe additive, and the outstanding content protection performance can beobtained.

In the liquid food filling field which carries out this invention,web-like paper packaging material is formed in the longitudinaldirection at a tube shape, filled products, such as fruit juice, tea,and liquid dairy products, are packed in tube-like packaging material,tube-like packaging material is transversal sealed for everypredetermined spacing in the transversal direction, packaging materialis cut along with a transversal-seal portion, and a brick shape paperpackaging container is obtained. Moreover, paper packaging material iscut in a predetermined configuration, the blanks which is sealed tocontainer lengthwise is obtained, after sealing the bottom of theblanks, the filling liquid product is packed from top opening, the upperpart is sealed, and the paper packaging container of a gable top shapeis obtained.

The example of the paper container in this invention includes thecontainer made of a converted paper (containers, such as a dress type, atwo-piece type, and a three-piece type), a composite can, an insertmolding container, a double container, etc. In the above case, thepackaging material is punched as the expansion plan of a papercontainer, and after carrying out creasing-line processing, thepackaging material is formed by the paper container of various forms byfolding and sealing along with a creasing line. As the seal method,there are heat sealing, a flame seal, a hot-air seal, an ultrasonicseal, a high-frequency-induction-heating seal, etc. The laminates aresupplied to a roll shape, a sleeve shape, or a cup shape, after beingfilled with a content, laminates are sealed using the variousabove-mentioned seal methods, and a paper container is formed in thefilling machine.

The manufacturing method of the packaging material for paper containersby this invention is described below.

The lamination method of usual packaging material includes a wetlamination-process, dry lamination-process, and non-solvent type drylamination process, an extrusion lamination process, the T diecoextrusion forming method, a coextrusion lamination process, a filmblowing, others, etc. In this invention, if required at theabove-mentioned lamination, pretreatment of, for example, a coronatreatment, ozonization, etc. can be carried out to the film. Forexample, anchor-coat agents, such as isocyanate (urethane), polyethyleneimine, poly butadiene, and organic titanium, lamination adhesives, suchas polyurethane, poly acrylic, polyester, epoxy, polyvinyl acetate, andcellulose, well-known anchor-coat agents, etc. can be used.

As mentioned above, in this invention, although the various laminationmethods are possible, in case packaging material is manufactured usingan extruding lamination process, more merits by this invention can beobtained in the laminated packaging material by this invention.

In the preferable embodiment by this invention, since the resin to beextruded and laminated has the properties parameter adjusted the optimalin the average density, the peak melting point, the melt flow index, theswelling ratio, and the layer thickness, and, for the reason, theextrusion-laminating properties and the good converting properties inpackaging material manufacture are shown.

In the manufacturing method of packaging material, more than thethermoplastic material outermost layer, the adhesives layer, theadhesive thermoplastic material layer, and the thermoplastic materialinnermost layer concerning this invention, an extrusion resin material,which constitutes the adhesive extruded layer, can be used. The materialincludes polyethylene, ethylene alpha-olefin copolymer, polypropylene,polybutene, poly isobutene, polyisobutylene, polybutadiene,polyisoprene, ethylene methacrylic-acid copolymer, copolymer ofethylene, such as ethylene acrylic acid copolymer, and unsaturatedcarboxylic acid, acid modified polyolefine resin, an ethylene ethylacrylate copolymer, ionomer resin, ethylene vinyl acetate copolymer,etc.

Moreover, specifically, the adhesives of the adhesives layer in the caseof using the dry-laminate method include urethane adhesives used in drylaminate etc., polyester urethane adhesives, polyether urethaneadhesives, acrylic adhesives, polyester adhesives, polyamide adhesives,polyvinyl acetate adhesives, epoxy adhesives, rubber adhesives, etc.

An example of the packaging material by this invention is shown inFIG. 1. The packaging material of the example comprises of constitutionlayers of the thermoplastic material outermost layer 21, the papersubstrate layer 22, the adhesive thermoplastic material layer 23, thebarrier layer 24, the adhesives layer 25, and the thermoplastic materialinnermost layer 26.

The packaging material is packaging material with crease lines. Thepackaging material is formed by the tube shape by the longitudinal sealof a longitudinal direction, and a liquid food product is packed in thetube shape formed packaging material, the transversal seal of thetube-like packaging material is carried out in the transversaldirection, the packaging material is formed by the primary shape of apillow, is separately cut by fixed spacing, is fold along with creaselines, and is formed to the final brick shape.

The outline of an example of the filling machine, which is used for thelaminated packaging material according this invention, is shown in FIG.2. In the filling machine shown in this example, the roll shapepackaging material web 1 having a thermoplastic material innermost layeris wound-out, and is conveyed with rollers into inside of the fillingmachine. By the strip tape applicator 3, the strip tape 2 is sealed tothe end of a packaging material web. The packaging material web passesthrough the inside of a sterilization agent bath 4, it is sterilized,and the air knife 5 removes a sterilization agent. The packagingmaterial is formed to a tube shape with the forming roller 6. Liquidfood is packed from the filling pipe 7 in the tube, and packagingmaterial is sealed in the longitudinal direction by thelongitudinal-seal element 8. The packaging material is fastened by aseal jaw 10 and counter jaw 11 in a heat-sealing equipment, sending thistube below by the length equivalent to one packaging container.Simultaneously, the packaging material is heat sealed in the transversaldirection, and is continuously formed in the letter packaging container12 of a pillow. Succeeding, the cutting schedule portion of the sealzone of the connecting pillow type packaging container is cut, and thepackaging material is separated with a knife etc. in each packagingfilling container 13 on the down stream. The flap of the upper and lowersides of the separated container 14 is folded, and the container isformed in the packaging filling container 11 of the final form with thefinal folder 14.

In another example which manufactures the paper container of thisinvention, the blank plates for paper containers with the creasing lineof the predetermined shape of the packaging material by this inventionare punched, subsequently, the edges of a blank plate are welded andcontainers are manufactured. The container is put into a fillingmachine, the bottom portion is folded along with a predeterminedcreasing line, and a heat-sealing bottom is formed by hot-airprocessing. A food content is packed from top opening, the top portioncan be folded along with a predetermined creasing lines, the top partcan be heat sealed by hot-air processing, the gable top type top partcan be formed, and a packaging product container can be manufactured.The example given above is illustration of the container for packagingconcerning this invention, and this invention is not limited by them.

Although the embodiment which protects a packaging material edge on amonolayer strip tape is shown in FIG. 3, a strip tape can be made into alaminate in this invention. The figure of partial breakdown of theexample is shown in FIGS. 6(A) and (B). The strip tape comprises of alaminate of the central layer 32 of a high density polyethylene (HDPE),and the both-sides layer 31 and 32 of the sealing-surface layer fromthis invention, in the embodiment of (A). Moreover, the strip tapecomprises of a laminate of the polyester (PET) central layer 32, and thetwo-layer both-sides layers 31 a, b, 33 a, b of the sealing-surfacelayer by this invention, in the embodiment of (B).

Although the container for packaging concerning this invention can applyliquid products, such as cow's milk, a lactic-acid-bacteria drink,liquid soup, a fruit-juice drink, barley tea, green tea, oolong tea,liquor, a seasoning, medical supplies, cosmetics, a coating material,adhesives, ink, a developer, and an etching reagent, to packaging, it ispreferably the container for liquid food.

EXAMPLE

The following examples describe this invention concretely.

Example 1-1

The linear low density polyethylene (mLLDPE) of the narrow molecularweight distribution which is polymerized with the metallocene catalystand the low density polyethylene by the high pressure process wereblended. Fusion extruding of the layer of the blended adhesives ofaverage density of 0.910, 97-degree C. of peak melting point, melt flowindex of 15, swelling ratio of 1.5, and 13-micrometer of layer thicknesswas carried out to the whole surface of aluminum foil with thickness of9 micrometers. The linear low density polyethylene (mLLDPE) having thenarrow molecular weight distribution which was polymerized with themetallocene catalyst, and the low density polyethylene by the highpressure process were further blended. The thermoplastic materialinnermost layer obtained with the blend of average density of 0.907,96-degree C. peak of melting point, melt flow index of 14, swellingratio of 1.5, and 25-micrometer of layer thickness was laminated, andthe laminated film which comprises of aluminum foil/blended adhesiveslayer/thermoplastic material blended innermost layer was prepared.

Simultaneously, low density polyethylene (density=0.920 g/cm³, MI=5.1)by the high pressure process was extrusion coated by 330 degrees C. ofextrusion temperatures on the paper substrate (weight=320 g/m²) by 20micrometers in thickness, and the thermoplastic material outermost layerwas laminated. Subsequently, linear low density polyethylene (mLLDPE) ofthe narrow molecular weight distribution which was polymerized with themetallocene catalyst, and the low density polyethylene by the highpressure process were blended. Between the paper side of the low densitypolyethylene/paper substrate, and the aluminum foil side of the aluminumfoil laminate, fusion extruding of the adhesive thermoplastic materiallayer of the blend of average density of 0.920, 99-degree C. peakmelting point, melt flow index of 17, swelling ratio of 1.5, and12-micrometer layer thickness was carried out, the thermoplasticmaterial layer was laminated, and the laminated web packaging materialhaving laminated structure of being shown in FIG. 1 was obtained.

The liquid food-packaging container of brick shape was obtained by thefilling machine shown in FIG. 2, using the packaging material. About theobtained packaging container, the seal temperature range of thelongitudinal seal in the filling machine, the temperature range of atransversal seal, and seal strength were evaluated.

Example 1-2

Packaging material and the brick type paper container were produced likethe example 1-1 except having used the thermoplastic material whichblended the linear low density polyethylene (mLLDPE) of the narrowmolecular weight distribution which was polymerized with the metallocenecatalyst, and the low density polyethylene by the high pressure processinstead of the low density polyethylene by the high pressure process ofthe thermoplastic material outermost layer in an example 1-1. Theblended thermoplastic material had average density of 0.915, 95-degreeC. of peak melting point, melt flow index of 17, swelling ratio of 1.5,and 18-micrometer of layer thickness. Furthermore, the same evaluationas the above-mentioned example was performed about the obtained papercontainer and packaging filling. The pattern encaustic color printed bypaper-layer external surface penetrated the transparent thermoplasticmaterial outermost layer, and was vividly viewed from the outside withgloss.

Example 1-3

The packaging material and the brick type paper container were producedlike the example 1-1 except having used for a 8-micrometer polyesterfilm the barrier film which vapor deposited the silicone oxide (SiOxCy)by the plasma enhanced chemical vapor deposition instead of the aluminumfoil in an example 1-1. Furthermore, it is similarly estimated as anexample about the obtained paper container and packaging filling.

Comparative Example 1-1

The packaging material and the brick type paper container were producedlike the example 1-1 except having used the low density polyethylene(density=0.920 g/cm³, MI=5.1) by the high pressure process for thethermoplastic material innermost layer and adhesives layer in an example1-1. Furthermore, the same evaluation as the above-mentioned example wasperformed about the obtained paper container and packaging filling.

Comparative Example 1-2

The packaging material and the brick type paper container were producedlike the example 1-1 except having used a low density polyethylene(density=0.920 g/cm³, MI=5.1) by the high pressure process for theadhesives layer in an example 1, and having used a film which was madefrom the low density polyethylene by the film blowing and the adhesiveresin for the thermoplastic material innermost layer in an example 1.Furthermore, the same evaluation as the above-mentioned example wasperformed about the obtained paper container and packaging filling.

Comparative Example 1-3

The packaging material and the brick type paper container were producedlike the example 1 except having used the thermoplastic material whichblended the linear low density polyethylene (mLLDPE) of the narrowmolecular weight distribution which polymerized with the metallocenecatalyst, and the low density polyethylene by the high pressure processinstead of the thermoplastic material of the innermost layer in anexample 1-1. The blended thermoplastic material had average density of0.915, 95-degree C. of peak melting point, melt flow index of 17,swelling ratio of 1.3, and the 18-micrometer of layer thickness.Furthermore, the same evaluation as the above-mentioned example wasperformed about the obtained paper container and packaging filling.

Evaluation about the seal temperature range of the above-mentionedlongitudinal seal, the temperature range of a transversal seal, and sealstrength was performed for an example 1-1, 1-2, 1-3, and a comparativeexample 1-1, 1-2 and 1-3. Consequently, it was proved that the examplesare superior to comparative examples.

For example, comparison of the example 1-2 and the comparative example1-2 proved that the seal temperature range of the longitudinal sealexpanded in 80% or more to low temperature side, and good sealabilitywas shown, and the temperature range of a transversal seal expanded 20%or more, and the seal at the time of packaging filling became moreeasily and simple in the example 1-2. Furthermore, when the example 1-2was compared with the comparative example 1-2 about the seal strength ofa transversal seal, the strength will have been improved 30 to 40%.Moreover, the impurity sealability (performance of whether to be able tocarry out a seal good, even if impurities, such as an oxide and remainsfood, exist between the thermoplastic material innermost layers of thezone which should seal) of a thermoplastic material innermost layer wasevaluated. Consequently, the container of the example was excellent inthe impurity sealability.

Example 2-1

By the same lamination as an example 1-1, the laminated web packagingmaterial of laminated constitution of being shown in FIG. 1 wasobtained.

By the filling machine shown in FIG. 2, the liquid food fillingpackaging container of brick shape was obtained using the packagingmaterial and the strip tape 2 of laminated constitution of being shownin FIG. 6. The sealing-surface layer of the strip tape was the materialwhich blended the linear low density polyethylene (mLLDPE) of the narrowmolecular weight distribution which was polymerized with the metallocenecatalyst, and the low density polyethylene by the high pressure process.The sealing-surface layer was extruded to the PET film, and thelaminated strip tape of 10 mm width which comprises of a sealing-surfacelayer/a PET layer/a sealing-surface layer was obtained. The blendedmaterial had average density of 0.915, 96-degree C. of peak meltingpoint, melt flow index of 15, and swelling ratio of 1.49. Evaluation ofthe seal temperature range of the longitudinal seal in the obtainedpackaging container and a filling machine and seal strength wasperformed.

Example 2-2

The packaging material and the brick type paper packaging container wereproduced like the example 2-1 except having used the thermoplasticmaterial which blended the linear low density polyethylene (mLLDPE) ofthe narrow molecular weight distribution which was polymerized with themetallocene catalyst, and the low density polyethylene by the highpressure process instead of the low density polyethylene by the highpressure process of the thermoplastic material outermost layer in anexample 2-1. The blended thermoplastic material had average density of0.915, 95-degree C. peak melting point, melt flow index of 17, swellingratio of 1.5, and 18-micrometer layer thickness. Furthermore, evaluationabout the obtained paper packaging container and packaging filling wasperformed. The seal temperature range expanded no less than 80% aboutthe longitudinal seal.

Example 2-3

The packaging material and the brick type paper packaging container wereproduced like the example 2-1 except having used for the 8-micrometerpolyester film the barrier film which vapor deposited the carbon contentsilicone oxide (SiOxCy) by the plasma enhanced chemical vapor depositioninstead of the aluminum foil in an example 2-1. Furthermore, the sameevaluation as the above-mentioned example was performed about theobtained paper packaging container and packaging filling.

Comparative Example 2-1

The packaging material and the brick type paper packaging container wereproduced like the example 2-1 except having used the low densitypolyethylene (density=0.920 g/cm³, MI=5.1) by the high pressure processfor the thermoplastic material innermost layer and adhesives layer in anexample 2-1. Furthermore, the same evaluation as the above-mentionedexample was performed about the obtained paper packaging container andpackaging filling.

Comparative Example 2-2

The packaging material and the brick type paper packaging container wereproduced like the example 1 except having used for the adhesives layerin an example 2-1 the film which was laminated with the low densitypolyethylene by the film blowing, and the adhesive resin as athermoplastic material innermost layer using the low densitypolyethylene (density=0.920 g/cm³, MI=5.1) by the high pressure process.Furthermore, the same evaluation as the above-mentioned example wasperformed about the obtained paper packaging container and packagingfilling.

Comparative Example 2-3

The packaging material and the brick type paper packaging container wereproduced like the example 2-1 except having used the thermoplasticmaterial which blended the linear low density polyethylene (mLLDPE) ofthe narrow molecular weight distribution from polymerization with themetallocene catalyst, and the low density polyethylene by the highpressure process instead of the thermoplastic material of the innermostlayer in an example 2-1. The blended thermoplastic material had averagedensity of 0.915, 95-degree C. of peak melting point, melt flow index of17, the swelling ratio of 1.3, and 18-micrometer of layer thickness.Furthermore, the same evaluation as the above-mentioned example wasperformed about the obtained paper packaging container and packagingfilling.

Comparative Example 2-4

Instead of the strip tape by this invention in the example 2-1,packaging material and the brick type paper packaging container wereproduced like the example 1 except having used the conventional strip ofan intermediate layer's polyester (PET, and amorphous PET are included)and the double-sided layer of LDPE. Furthermore, the same evaluation asthe above-mentioned example was performed about the obtained paperpackaging container and packaging filling.

Evaluation of the seal temperature range of the above-mentionedlongitudinal seal and seal strength was performed about the examples2-1, 2-2, 2-3 and the comparative examples 2-1, and 2-2, 2-3 and 2-4.Consequently, it was shown that the examples are superior to comparativeexamples. For example, when the example 2-1 was compared with thecomparative example 2-1, in the example 2-1, the seal temperature rangeof a longitudinal seal expanded in 100% or more to lower temperatureside, good sealable ability was shown, and it was proved that the sealat the time of packaging filling became more easily and simple.Furthermore, when the example 2-2 was compared with the comparativeexample 2-2 about seal strength, it have improved 30 to 40%. When anexample 2-1, and 2, 3 and a comparative example 2-4 are compared, evenif the filling packaging speed using the filling machine by FIG. 2speeds up 70%, the good seal in a longitudinal-seal portion was shown inthe example. The workability of packaging filling improved.

Example 3-1

The low density polyethylene (density=0.920 g/cm³, MI=5.1) by the highpressure process was extrusion coated by 330 degrees C. of extrusiontemperatures on the paper substrate (weight=320 g/m²) by 20 micrometersin thickness, and the outside thermoplastic material layer waslaminated. Then, mLLDPE with the properties parameter of average densityof 0.925, 116-degree C. of peak melting point by the differentialscanning calorimetry, melt flow index of 10, and swelling ratio of 1.5was laminated at the inside rear face of a paper substrate by the35-micrometer layer thickness.

The packaging material was punched to the blank plate for paperpackaging containers with creasing lines, subsequently, the edges of theblank plates were welded and the sleeve shape container wasmanufactured. The container was put into the liquid food fillingmachine, the bottom portion was folded along with the predeterminedcreasing line, heat fusion was carried out by hot-air processing, thebottom was formed, and, subsequently the content product was packed fromtop opening. The top portion was folded along with the predeterminedcreasing line, heat fusion was carried out by hot-air processing, andthe gable top type packaging product was manufactured. The temperaturerange and seal strength of the top seal of the obtained packagingcontainer were evaluated.

Example 3-2

The packaging material and the paper packaging container were producedlike the example 1 except having used the blend polymer which blendedthe linear low density polyethylene (mLLDPE) of the narrow molecularweight distribution which polymerized with the metallocene catalyst, andthe low density polyethylene by the high pressure process instead ofmLLDPE of the inside thermoplastic material layer in an example 3-1. Theblend polymer of a 35-micrometer layer thickness had the propertiesparameter of average density of 0.925, 118-degree C. of peak meltingpoint by the differential scanning calorimetry, melt flow index of 11,and swelling ratio of 1.5. Furthermore, the same evaluation as theabove-mentioned example was performed about the obtained paper packagingcontainer and packaging filling.

Example 3-3

The packaging material and the paper packaging container were producedlike the example 1 except having used LLDPE of the 35-micrometer layerthickness which has the properties parameter of average density of0.925, 118-degree C. of peak melting point by the differential scanningcalorimetry, melt flow index of 11, and swelling ratio of 1.5 instead ofmLLDPE of the inside thermoplastic material layer in an example 3-1.Furthermore, the same evaluation as the above-mentioned example wasperformed about the obtained paper packaging container and packagingfilling.

Comparative Example 3-1

The packaging material and the paper packaging container were producedlike the example 3-1 except having used the low density polyethylene(density=0.923, MFI=4, 113-degree C. of peak melting point by thedifferential scanning calorimetry, 1.8 of swelling ratios) by the highpressure process instead of mLLDPE of the inside thermoplastic materiallayer in an example 3-1. Furthermore, the same evaluation as theabove-mentioned example was performed about the obtained paper packagingcontainer and packaging filling.

Comparative Example 3-2

Instead of mLLDPE of the inside thermoplastic material layer in anexample 3-1, packaging material and the paper packaging container wereproduced like the example 3-1 except having used the low densitypolyethylene (density=0.925, MFI=3, the 110-degree C. of peak meltingpoint by the differential scanning calorimetry, 1.7 of swelling ratio).Furthermore, the same evaluation as the above-mentioned example wasperformed about the obtained paper packaging container and packagingfilling.

An above-mentioned top seal temperature range and its above-mentionedseal strength were evaluated for the examples 3-1, 3-2, 3-3, and thecomparative examples 3-1 and 3-2. Consequently, it was proved thatexamples are superior to comparative examples.

For example, when the example 3-1 was compared with the comparativeexample 3-1, in the example 3-1, the temperature range of a sealexpanded 20% or more, and the seal at the time of packaging fillingbecame more easily and simple. In the example 3-1, the ratio of leakageof samples was 0% about the top seal strength. On the other hand, sincepinhole, foaming, the blister, etc. occurred in the fused thermoplasticmaterial layer, 5–10% of the samples of the comparative examples showedleakages.

Moreover, the impurity sealability (performance of whether to be able tocarry out a seal good, even if impurities, such as an oxide and remainsfood, exist between the thermoplastic material innermost layers of thezone which should seal) of a thermoplastic material innermost layer wasevaluated. Consequently, those containers were excellent in the impuritysealability.

As the above-mentioned examples proved, this invention shows thefollowing effectiveness.

The packaging material for paper containers of this invention has goodperformance in an extrusion-laminating properties required in the caseof packaging material manufacture, and the converting properties by it,and manufacture of packaging material is easy for it. Packaging materialcan be heat sealed quickly, tougher seal strength is made possible, anda good seal is obtained, without receiving influence in the temperatureof a content product. That is, impurity sealable ability improves andthe seal performance is excellent. The container has a non-scalping or aquality preservability.

Moreover, a good seal is obtained also at low temperature also with hightemperature, without receiving influence in the temperature of a contentproduct, since a seal temperature range expands at the time of packagingfilling. For example, since the seal temperature in a filling machinecan be set as temperature lower than the usual temperature, even if thethin film layer of an inorganic oxide, the thin film layer of analuminum, etc. are used for a barrier layer, a heat damage can bereduced, as a result barrier degradation can be prevented.

In this invention, at the time of a seal, a pinhole, foaming, a blister,etc. do not happen in the thermoplastic material layer for seals, butseal strength can be maintained, and there is no leakage of a liquidcontent. Therefore, filling packaging to a low cost paper packagingcontainer is easy, and can heat seal quickly. Tougher seal strength ismade possible, and a good seal is obtained, without receiving influencein the temperature of a content product, and the container has anon-scalping or a quality preservability.

INDUSTRIAL APPLICABILITY

From the packaging material by this invention, the packaging containerin which liquid food, such as cow's milk and a fruits drink, are put canbe manufactured.

1. A packaging material for making paper containers having an interiorcomprising at least a thermoplastic material outermost layer, a papersubstrate layer, a barrier layer, and a thermoplastic material innermostlayer in such order, the innermost layer being adapted to be locatedcloser to the interior of the paper container than the outermost layerwhen the packaging material is formed into the paper container, thethermoplastic material innermost layer containing at least a linear lowdensity polyethylene which has an average density of 0.900 g/mL–0.915g/mL, a peak melting point of 88° C. to 103° C., a melt flow index of 5dg/min–20 dg/min, a swelling ratio of 1.4–1.6, and a layer thickness of20–50-micrometer.
 2. A packaging material for paper containers accordingto claim 1, wherein the thermoplastic material outermost layer containsat least a linear low density polyethylene which has an average densityof 0.900 g/mL–0.925 g/mL, a peak melting point of 88° C. to 103° C., amelt flow index of 5 dg/min–20 dg/min, a swelling ratio of 1.4–1.6, anda layer thickness of 10–25 micrometer.
 3. A packaging material for papercontainers according to claim 1, including an adhesives layer betweenthe barrier layer and the thermoplastic material innermost layer thatcontains at least a linear low density polyethylene which has an averagedensity of 0.900 g/mL–0.915 g/mL, a peak melting point of 88° C. to 103°C., a melt flow index of 5 dg/min–20 dg/min, a swelling ratio of1.4–1.6, and a layer thickness of 2–15 micrometer.
 4. A packagingmaterial for paper containers according to claim 1, including anadhesive thermoplastic material layer between the paper substrate layerand the barrier layer which contains at least a linear low densitypolyethylene which has an average density of 0.890 g/mL–0.925 g/mL, apeak melting point of 88° C. to 103° C., a melt flow index of 10dg/min–20 dg/min, a swelling ratio of 1.4–1.6, and a layer thickness of10–25 micrometer.
 5. A paper packaging container formed from a packagingmaterial comprising at least a thermoplastic material outermost layer, apaper substrate layer, a barrier layer, and a thermoplastic materialinnermost layer in such order, the innermost layer being located closerto an interior of the packaging container than the outermost layer, thethermoplastic material innermost layer containing at least a linear lowdensity polyethylene which has an average density of 0.900 g/mL–0.915g/mL, a peak melting point of 88° C. to 103° C., a melt flow index of 5dg/min–20 dg/min, a swelling ratio of 1.4–1.6, and a layer thickness of20–50 micrometer; a strip tape covering a discontinuous section of thethermoplastic material innermost layer between two edges of thepackaging material in a liquid tight manner, and at least asealing-surface layer of the strip tape containing a linear low densitypolyethylene which has an average density of 0.900 g/mL–0.915 g/mL, apeak melting point of 88° C. to 103° C., a melt flow index of 5dg/min–20 dg/min, a swelling ratio of 1.4–1.6, and a layer thickness of20–100 micrometer.
 6. A paper packaging container formed from apackaging material comprising at least an outside thermoplastic materiallayer, a paper substrate layer, and an inside thermoplastic materiallayer, in such order, the inside thermoplastic material layer containingat least a linear low density polyethylene, and having an averagedensity of 0.910 g/mL–0.930 g/mL, a peak melting point of 115 degrees°C. or more by differential scanning calorimetry, a melt flow index of 5dg/min–15 dg/min, and a swelling ratio of 1.45–1.55.
 7. The packagingmaterial of claim 1, wherein the thermoplastic material innermost layeris extrusion laminated.
 8. The paper packaging container of claim 5,wherein the thermoplastic material innermost layer is extrusionlaminated.
 9. The paper packaging container of claim 6, wherein theinside thermoplastic material layer is extrusion laminated.